1. Field of the Invention
The present invention relates to a vehicle crane in which the counterweight assembly is coupled to the jib by means of a coupler, such that the position of the counterweight assembly depends on the tilt position of the jib.
Arranging counterweights on the turntable of vehicle cranes in order to counter and at least reduce the moment acting on the turntable from a load on the jib is known from the prior art. Vehicle cranes comprising counterweights that can be varied in their position relative to the turntable, in order to cope with different load conditions on the jib, are also known from the prior art.
2. Description of the Related Art
U.S. Patent Application Publication No. 2008/0099421 discloses a vehicle crane, in particular a crawler crane, in which the counterweights can be moved relative to the turntable by means of a hydraulic cylinder. The position of the counterweight is preferably controlled by computer control. While this moveable counterweight system provides many advantages, there are some instances when a simpler system is more desirable.
U.S. Pat. No. 6,341,665 discloses a movable work platform comprising a jib and a counterweight assembly. In the disclosed aerial work platform, the position of the counterweight assembly relative to the turntable is fixedly coupled to the tilt angle of the jib by means of a lever mechanism, hydraulic cylinders or motors. The proposed counterweight assembly, being close to the tilt axis of the jib, is however less suitable for vehicle cranes such as mobile telescoping cranes, since the amount of counterweight would otherwise have to be increased to generate sufficient counterweight moment. However, due to the maximum allowable weight of the mobile telescoping crane designed to travel over roads, increasing the amount of counterweight would necessitate weight reductions elsewhere, which would ultimately lead to a reduced working load of the vehicle crane. However, if the counterweights are arranged further away from the tilt axis of the jib, there is a danger of the working range of the crane being restricted, since the counterweight would be moved a very long way backwards when the jib is tilted out to its maximum extent.